This invention relates to methods for manufacturing pellet-like semiconductor elements, such as diodes, transistors and ICs, that are formed by dicing a wafer with metal electrode films formed on the wafer surfaces. More particularly, the invention relates to methods for manufacturing semiconductor elements in which burrs projecting from the metal electrode films which are produced by the dicing process are removed from the outer surfaces of the semiconductor elements.
FIG. 11 shows schematically the general arrangement of a mesa semiconductor diode which is one type of semiconductor element. As is well known, this diode has a p-type layer 1b which is formed by diffusing boron into the surface of one of the major sides of a silicon body 1 having, for example, an n-type layer 1a, and it includes metal electrode films 2 and 3 formed on the major sides of the body 1, respectively.
FIG. 12 shows a silicon wafer 1A used to produce the semiconductor element 1 in which a p-type layer is formed on one of the major sides of the silicon wafer. Further, the wafer has metal electrode films 2A and 3A on opposite sides which are formed by a vapor deposition process, for example.
FIG. 13 shows a process for manufacturing a number of diodes D from the silicon wafer 1A. As shown in FIG. 13, the major side of the silicon wafer 1A having the metal electrode film 3A is equidistantly grooved in the vertical and horizontal directions by an etching process. This produces equidistantly spaced sets of perpendicular grooves 4 which define a number of square pieces, each including a portion 3 of the metal electrode film 3A. The grooved silicon wafer 1A, including the metal electrode film 2A, is then diced along the grooves 4 by a diamond cutter 5, for example, to form a number of square pieces, or semiconductor diodes D, each having a substrate 1 sandwiched between metal electrode films 2 and 3.
Silver (Ag) has been used widely for electrodes for this type of semiconductor element, i.e., for the metal electrode films 2 and 3 of the diodes D in the illustrated example. Silver not only has excellent electrical conductivity, but also has good malleability and ductility. Because of its good malleability and ductility, silver functions advantageously in that it is easy to work in the manufacture of semiconductor elements. However, because of its good ductility, the portions of the metal electrode film 2A which are cut by the diamond cutter 5 in the wafer dicing process project away from the element as burrs a.
The length of the burrs a produced in the wafer dicing process depends on the thickness of the silver electrode film 2A. For example, it has been experimentally determined that, for an electrode film 2A 6 to 10 .mu.m thick, the burrs a formed by the dicing process were 10 to 80 .mu.m long.
To assemble such semiconductor elements into electronic parts, an assembling jig 8, shown in FIG. 14, is usually used. The jig 8 is constructed with a recess 6 in which a semiconductor element, i.e., the diode D in this example, is to be set against a surface 6a and includes a suction hole 7 which opens into the recess 6. When a diode D with a burr a projecting from the metal electrode film 2A is set in the recess 6, the diode D is tilted because the burr is brought into contact with the surface 6a of the recess 6 as shown.
In the suction step, a vacuum pump, not shown, draws air through the suction hole 7 to pull the diode D against the surface 6a. However, because the burr a holds the diode D tilted in the recess 6 leaving a gap, the bottom surface of the metal electrode film 2A of the diode is not drawn against the surface 6a. This makes it difficult to assemble the semiconductor elements.
To overcome the problem produced by the burr a, the prior art, so far as we know, has (1) made the silver electrode film 2A as thin as possible, thereby forming a burr of the smallest possible height from the electrode surface, and (2) used an electrode film 2A of normal thickness and etched away the burr formed after dicing by an etching solution of aluminum nitrate, for example.
The first measure succeeds in reducing the height of the burr since the electrode film 2A of the wafer 1A is reduced in thickness. However, this measure does not avoid the problem of loose contact because, when the electrode film 2A is soldered to a lead (not shown) during assembly of the diode D, silver from the electrode film is also partially softened or melted away by heat from the solder.
The second measure for removing the burr by an etching process also tends to suffer from the loose contact problem because the etching solution may reach the electrode film 2A so as to corrode the silver in the electrode film as well as reducing the burr a.